The invention concerns a laminated core with laminations arranged on top of each other which each are connected to each other by a first connection as well as methods for its manufacture wherein, from a metal strip, laminations are punched and subsequently stacked to a laminated core, wherein the laminations may be provided with projections and depressions for force-locking or may be connected by a weld seam.
Laminated cores are used in electric machines, for example as stators or rotors for electric motors or generators.
The laminated cores are comprised of laminations arranged on top of each other and punched from a metal strip.
The manufacture of the laminated core can be realized in various ways outside or inside a punching tool. The laminations seated on each other are connected to each other by means of a first connection. This first connection can be a mechanical connection, an adhesive connection or a weld connection. In case of the mechanical connection, the laminations are provided with projections or embossments with which they engage appropriate cutouts or depressions of the lamination below, respectively. In case of an adhesive connection, the laminations that are resting on each other are connected to each other by an adhesive. In case of a weld connection, the laminations that are arranged on top of each other are welded to each other within the laminated core.
Apart from the advantages, the respective aforementioned employed conventional kinds of connection for producing laminated cores during the punching operation have also disadvantages however. The important advantage in punch stacking is the very quick connection of the individual laminations to a core. The disadvantages are the generation of short-circuit links within a core as well as a minimal tensile strength.
Electric short-circuits are also caused when manufacturing the laminated core by welding the laminations. Furthermore, the laminated core deforms due to thermal warping in the weld seam vicinity. Also, a change of the microstructure takes place due to the high processing temperatures in the welding zone. This can cause an uncontrolled effect on the magnetic flux during future use of the laminated core in the electric machine.
Short-circuit links generally cause magnetic loss which negatively affects the efficiency of a motor/generator.
Adhesive connections produced during a punching operation have the important advantage that they do not generate short-circuit links within a core. However, due to the high processing speed in processing electrical steel strips of up to 700 strokes per minute in the punching operation, it is mandatorily required to employ fast-curing adhesive systems. In this context, adhesives with an adhesive system are used which then preferably cure by moisture in the air, temperature or activator.
Instant adhesives that cure by moisture in the air do not have high temperature resistance and chemical resistance. The temperature-curing adhesives are generally very slow and can be used only conditionally for adhesively connecting the laminations during punching. Moreover, a high expenditure is required for core separation during the punching process. Also, the thermal separation or cooling of the joining unit relative to the punching tool and the punching press is very complex.
When using adhesive systems in connection with an initiator/activator, the media application in the punching process is performed preferably on separate sides of the electric steel strip. By using initiator/activator, high processing speeds can be achieved. The important disadvantage resides in maintaining the ideal mixing ratio and the optimal positioning of and between the adhesive and initiator/activator during the punching process. This application process can only be realized and/or monitored with very high technical expenditure and the associated very high costs. Furthermore, additional space within the punching press or punching tool is required for this equipment. Therefore, the efficiency of the punching machine drops significantly.
It is the object of the invention to configure the laminated core of the aforementioned kind and the method of the aforementioned kind in such a way that the laminated cores can be produced in a simple way such that, on the one hand, they can be handled very quickly, on the other hand, have a high resistance in respect to the further processing steps and the efficiency in use in an electrical machine is improved.